Investments - Schedule of Fair Value of Financial Instruments Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities
Available-for-sale Securities	$ 937,812	$ 834,531
U.S. Government and Agency Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	102,729	92,626
Foreign Government
Schedule of Available-for-sale Securities
Available-for-sale Securities	2,966	2,036
States, Municipalities and Political Subdivisions
Schedule of Available-for-sale Securities
Available-for-sale Securities	151,866	201,512
Public Utilities
Schedule of Available-for-sale Securities
Available-for-sale Securities	24,142	20,257
Corporate Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	289,596	287,562
Mortgage-backed securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	204,990	143,265
Asset-backed Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	58,898	14,905
Redeemable Preferred Stocks
Schedule of Available-for-sale Securities
Available-for-sale Securities	1,203	692
Fixed Maturities
Schedule of Available-for-sale Securities
Available-for-sale Securities	836,390	762,855
Public Utilities
Schedule of Available-for-sale Securities
Available-for-sale Securities	2,357	1,702
Common Stock
Schedule of Available-for-sale Securities
Available-for-sale Securities	37,568	27,902
Nonredeemable Preferred Stocks
Schedule of Available-for-sale Securities
Available-for-sale Securities	2,072	1,767
Equity Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	93,092	63,295
Other Long-term Investments
Schedule of Available-for-sale Securities
Available-for-sale Securities	8,330	8,381
Mutual Fund
Schedule of Available-for-sale Securities
Available-for-sale Securities	51,095	31,924
Level 1
Schedule of Available-for-sale Securities
Available-for-sale Securities	94,213	64,287
Level 1 | U.S. Government and Agency Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 1 | Foreign Government
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 1 | States, Municipalities and Political Subdivisions
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 1 | Public Utilities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 1 | Corporate Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 1 | Mortgage-backed securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 1 | Asset-backed Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 1 | Redeemable Preferred Stocks
Schedule of Available-for-sale Securities
Available-for-sale Securities	821	692
Level 1 | Fixed Maturities
Schedule of Available-for-sale Securities
Available-for-sale Securities	821	692
Level 1 | Public Utilities
Schedule of Available-for-sale Securities
Available-for-sale Securities	2,357	1,702
Level 1 | Common Stock
Schedule of Available-for-sale Securities
Available-for-sale Securities	37,568	27,902
Level 1 | Nonredeemable Preferred Stocks
Schedule of Available-for-sale Securities
Available-for-sale Securities	2,072	1,767
Level 1 | Equity Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	93,092	63,295
Level 1 | Other Long-term Investments
Schedule of Available-for-sale Securities
Available-for-sale Securities	300	300
Level 1 | Mutual Fund
Schedule of Available-for-sale Securities
Available-for-sale Securities	51,095	31,924
Level 2
Schedule of Available-for-sale Securities
Available-for-sale Securities	837,742	769,610
Level 2 | U.S. Government and Agency Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	102,729	92,626
Level 2 | Foreign Government
Schedule of Available-for-sale Securities
Available-for-sale Securities	2,966	2,036
Level 2 | States, Municipalities and Political Subdivisions
Schedule of Available-for-sale Securities
Available-for-sale Securities	151,866	201,512
Level 2 | Public Utilities
Schedule of Available-for-sale Securities
Available-for-sale Securities	24,142	20,257
Level 2 | Corporate Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	289,596	287,562
Level 2 | Mortgage-backed securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	204,990	143,265
Level 2 | Asset-backed Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	58,898	14,905
Level 2 | Redeemable Preferred Stocks
Schedule of Available-for-sale Securities
Available-for-sale Securities	382	0
Level 2 | Fixed Maturities
Schedule of Available-for-sale Securities
Available-for-sale Securities	835,569	762,163
Level 2 | Public Utilities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 2 | Common Stock
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 2 | Nonredeemable Preferred Stocks
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 2 | Equity Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 2 | Other Long-term Investments
Schedule of Available-for-sale Securities
Available-for-sale Securities	2,173	7,447
Level 2 | Mutual Fund
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3
Schedule of Available-for-sale Securities
Available-for-sale Securities	5,857	634
Level 3 | U.S. Government and Agency Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Foreign Government
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | States, Municipalities and Political Subdivisions
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Public Utilities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Corporate Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Mortgage-backed securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Asset-backed Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Redeemable Preferred Stocks
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Fixed Maturities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Public Utilities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Common Stock
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Nonredeemable Preferred Stocks
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Equity Securities
Schedule of Available-for-sale Securities
Available-for-sale Securities	0	0
Level 3 | Other Long-term Investments
Schedule of Available-for-sale Securities
Available-for-sale Securities	5,857	634
Level 3 | Mutual Fund
Schedule of Available-for-sale Securities
Available-for-sale Securities	$ 0	$ 0